Synthesis, Assembly And Photoelectrical Properties Of Electrospun Oxide Nanofibers

One-dimensional (1D) semiconducting oxides with a wide bandgapare chemically stable, highly sensitive, fast-response and portable, which areideal candidates for the next-generation high-performance ultraviolet (UV)photodetectors. Synthetic methods based on vapor/liquid phase have difficultiesin device-assembly, controlling the doping concentration as well as large-scaleproduction. Electrospinning is a facile and effective techique in fabricatingcontinuous nanofibers in a scalable way and has already been commercialized.With a modified collector, highly aligned nanofibers can be obtained andintegrated into functional devices. Moreover, by adjusting the composition ofprecursor solutions, nanofibers with versatile morphology and precise dopingcontents can be achieved.In this thesis, In2O3and NiO nanofibers， SnO2nanobelts and ZnOnanorod-on-nanotube hierarchical complex nanostructures have beensynthesized via electrospinning. Using a simple collector, highly orientednanofibers were collected and integrated into photoresistors， field effecttransistors (FETs) and heterojunction photodiodes. It is found that native andimpurity-induced defects as well as the device configuration can greatlyinfluence the electrical and optoelectrical properties of1D semiconductingoxides. The main achievements are listed as follows:In2O3nanofibers with high aspect ratios were prepared and assembled inton-type FETs and photoresistors. The electrospun In2O3nanofibers demonstratedincreased electron concentration and dual-band photoresponse, which areattributed to the existence of a large number of native oxygen vacancies in thenonstoichiometric In2O2.68nanofibers.A series of Ni-doped SnO2nanobelts were fabricated. We found that Nidoping can greatly affect the crystallinity, phase composition and photoresponseproperties of SnO2nanobelts, resulting in an obvious enhancement in bothphotosensitivity and recovery speed.A well-defined heterojunction photodiode based on SnO2nanobelts/NiO thin film was constructed by electrospinning and spincoating. This p-n junctiondiode demonstrates stable rectifying characteristics as well as greatly enhancedUV photoresponse, which exhibits ultrahigh photosensitivity up to105withimproved response speed under reverse bias. Besides, this heterojunction showshigh optical transparency, which makes it a promising candidate forhigh-performance transparent photodiode.We demonstrated that SnO2nanobelt network has high optical transparencyand superior bending/stretchable flexibility. This free-standing nanobeltnetwork can be easily integrated into various soft or curved substrates andexhibits stable UV photoresponse while being bent or stretched, which can beapplied in transparent and flexible optoelectrical devices.